浅谈自定义注解在Spring中的应用

@Target({ ElementType.TYPE })
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Component
public @interface MyComponent {
  String value() default "";
}

@Configuration
public class ComponentAnnotationTest {
 public static void main(String[] args) {
  AnnotationConfigApplicationContext annotationConfigApplicationContext = new AnnotationConfigApplicationContext();
annotationConfigApplicationContext.register(ComponentAnnotationTest.class);
  annotationConfigApplicationContext.refresh();
  InjectClass injectClass = annotationConfigApplicationContext.getBean(InjectClass.class);
    injectClass.print();
 }
 @MyComponent
 public static class InjectClass {
  public void print() {
    System.out.println("hello world");
  }
 }
}

A component provider that scans the classpath from a base package. 
It then applies exclude and include filters to the resulting classes to find candidates.

protected void registerDefaultFilters() {  
  this.includeFilters.add(new AnnotationTypeFilter(Component.class));
  ClassLoader cl = ClassPathScanningCandidateComponentProvider.class.getClassLoader();
  try {  
   this.includeFilters.add(new AnnotationTypeFilter(((Class<? extends Annotation>) ClassUtils.forName("javax.annotation.ManagedBean", cl)), false)); 
   logger.debug("JSR-250 'javax.annotation.ManagedBean' found and supported for component scanning"); 
  }  catch (ClassNotFoundException ex) {   
   // JSR-250 1.1 API (as included in Java EE 6) not available - simply skip.  
  }  
  try {   
   this.includeFilters.add(new AnnotationTypeFilter(((Class<? extends Annotation>) ClassUtils.forName("javax.inject.Named", cl)), false));   
   logger.debug("JSR-330 'javax.inject.Named' annotation found and supported for component scanning");  
  } 
  catch (ClassNotFoundException ex) {   
  // JSR-330 API not available - simply skip. 
  }
}